The present invention relates generally to telecommunications, and more specifically to wireless communication systems.
In connection with mobile communication systems, it is becoming increasingly important to determine the location of the communicating Mobile Unit. Various systems for locating are already well known. One solution that is readily available in most modern cellular systems is to use the ID of the cell from which the mobile unit is communicating. Typically, this information is accurate to a resolution of several miles. A second solution is to compute the location of the mobile unit based on the cellular network signaling parameters (angle of arrival or time difference of arrival). This information is typically accurate to hundreds of meters. Yet another solution is to equip the mobile unit with a GPS receiver which then attempts to track the location of the mobile unit as accurately as possible. Typically, GPS receivers can compute locations to within several tens of meters of accuracy. When combined with differential corrections, the GPS accuracy can be improved.
As far as reliability is concerned, the cell ID information is the most reliable, and is guaranteed to be available as long as the cellular network is functioning normally. The network signal based location computations are less reliable, since they are dependent on several conditions being true at the time of the call. For example, most schemes require the mobile unit to have line-of-sight visibility to multiple cellular base stations. This is not always possible. GPS based location computation is also not always reliable since the mobile unit may be in an environment where there is no penetration of the GPS satellite signals.